Combustion process with ionization control

ABSTRACT

Process and burner tip of an oil burner, in particular for carrying out the said process, for generating a sootless flame in pressure atomizer oil burners operating with oil atomizing cones, wherein the geometrical shape as regards length and width of the flame is determined by associating two channels (13, 24) guiding combustion air into a flame area and wherein the air volume supplied into each of the channels (13, 24) can be varied separately for the purpose of imparting to the combustion air a different whirl.

DESCRIPTION OF THE PRIOR ART

The invention starts out from a process for generating a sootless flamein pressure atomizer burners producing an oil atomizing cone, and/or aburner tip of an oil burner, in particular for carrying out the processof the present invention, according to the species described in claim 4.

Until recently, one of the main problems in generating sootless flameslay in the difficulty to keep the flames, in spite of the required highair velocities and the high atomizing pressure, sufficiently short toobtain the at least fairly uniform surface loading required forsatisfactory efficiency.

There have been known a process for generating a short sootless flame(German Patent Document No. 32 28 452.7) and a burner tip of an oilburner, in particular for carrying out the said process, in which aricher air/oil mixture for a luminous flame is achieved by a first aircurrent catching the oil atomizing cone and in which a second whirledair current is introduced transversely to the said first air current inorder to shorten the flame and burn any residual unburnt particles. Theyellow portion permits optical monitoring of this flame. However, it hasbeen found in practice that in firing equipment with low flue gastemperatures it is desirable that the fired boiler walls should beheated as uniformly as possible, a requirement which can be fulfilled toa very limited degree only by the known processes and burner tips. Inparticular, the relation between the yellow flame and the amount ofsecondary air introduced for producing a blue flame is confined to veryclose tolerance limits. In the case of blue flames and flame monitoringby the ionization principle, an ionizable gas mixture must occur in thearea of the monitoring sensor. A gas flame is capable of conductingcurrent, producing at the same time a rectifier effect, so that analternating current applied may be transformed into a direct currentover the gas flame or the ionization mixture. In the case of the knownlong blue flames it is therefore necessary to arrange the ionizationelectrodes or the electrode at a point where ionization is alwaysguaranteed, i.e. in the case of the long flames at a point relativelyfar away from the oil nozzle.

It is a substantial problem of the known oil burners operating with ablue flame that the before-described processes necessary for generatingthe blue flame favor the so-called breaking of the flame which causesthe burner to indicate a fault condition.

Another considerable disadvantage of the known oil burners consists inthe fact that the attempt to make the flame as short as possible and, inaddition, to achieve additional heat accumulation for improved airpreparation by the use of ceramic tubes, leads to coking effects at theoil burner nozzle due to which the atomizing cone or even the atomizingorifice may be deformed in an adverse manner.

OBJECT OF THE INVENTION

Now, it is the object of the present invention to provide a combustionprocess and/or a burner tip for carrying out the said process, in whichthe geometry of the flame can be adapted to the firing space to obtainimproved efficiency, in which no coking effects are obtained in thenozzle area and which can be supplied as simple compact unit for oilburners of different types.

ADVANTAGES OF THE INVENTION

This object is achieved by the characterizing features of the main claimand of claim 4 which offer the advantage that the geometrical dimensionsof the flame can be fully varied by extremely simple means, i.e. bychanging the air volume entering through the cylindrical wall and/or thebottom of the flame bowl, without thereby impairing the combustionquality. The particular way in which the air enters at the bottom of theflame bowl prevents any coking in the nozzle area and this the more asadditional heat accumulation means are rendered superfluous through theparticular way in which the air is whirled. Due to the fact that theflame is retracted through the entry of air into the bowl, without thebowl wall being overheated, both the ionization control system and theignition electrodes may be arranged within the flame bowl whereby acompact burner tip is obtained which is economical to produce and whichprovides trouble-free operation. The blue flame thus obtained burnsfreely without any additional flame guide and does not tend to produceresonance phenomena; its noise level is low. Moreover, the tipcomponents are no longer stressed by high temperatures.

According to an advantageous improvement of the invention, the oilnozzle is slightly recessed relative to the bottom of the flame bowl sothat the entering primary air gets immediately below the oil atomizingcone and screens the flame against the nozzle outlet.

According to an additional advantageous improvement, the spiral-shapedchannel comprises radial inlets and/or outlets and is arrangedpreferably in a ring insert whereby the helically whirled incoming aircatches the oil atomizing cone at its very beginning so that a flamecone can form immediately downstream of the inlet opening of the oilnozzle.

According to an advantageous improvement, the secondary air whirlingmeans is arranged upstream of the flow connection between the annularchannel and the interior of the flame bowl, and the whirling directionis substantially equal. Accordingly, the whirl of the secondary air hasthe effect to intensify the whirl produced by the slot-shaped channelsin the cylindrical portion of the flame bowl.

According to a further improvement of the invention, the bottom of theflame bowl is stepped or crowned in shape and comprises an outer annularportion which is recessed in the flow direction and receives thesensors, and a projecting inner annular portion receiving the primaryair guide (ring insert 12). This prevents in an advantageous manner sootfrom depositing on the bottom which is cooled by the air current, assuch deposition of soot may lead to failures of the flame control or ofthe air flow.

Further advantages of the invention will be apparent from the followingdescription of an example, the drawing and the claims.

DESCRIPTION OF THE DRAWING

Two variants of one embodiment of the subject-matter of the inventionare shown in the drawing and will be described hereafter in detail. Inthe drawing

FIG. 1 shows a longitudinal cross-section through a burner tip accordingto the invention;

FIG. 2 shows a cross-section taken along line II in FIG. 1; and

FIG. 3 shows a partial cross-section according to FIG. 1, through thesecond variant.

DESCRIPTION OF THE EMBODIMENT

A burner nozzle assembly 1 with oil burner nozzle is clamped coaxiallyin a burner tip insert 3 mounted coaxially with a jacket tube 4 of theburner tip.

The jacket tube 4 is mounted with its side 5 in the housing of afan-type oil burner so that air can be introduced at a certain pressure(fan pressure) in the direction of arrow I. The burner nozzle assembly 1is connected with an oil line 6 through which fuel oil is supplied tothe burner nozzle 2. On the side opposite the entry side 5, the firetube 4 is drawn inwardly through a conical portion 7 so that a finaloutlet air cross-section 8 is obtained.

The burner tip insert 3 which is shown partly in cross-section,comprises a flame bowl 9 having a cylindrical portion 10 and a flamebowl bottom 11. The wall of the flame bowl bottom 11 is perforated inthe area of the oil burner nozzle 2. A whirl ring insert 12 is supportedby the wall of such perforation and pressed from below against the bowlbottom 11 by the oil burner nozzle 2. The ring 12 is exchangeable andcomprises helically shaped slot-like channels 13 comprising sectors withradial inlet and/or outlet openings. This makes it possible, byexchanging the ring 12, to pre-determine firstly the direction andsecondly the volume of the air entering the flame bowl via the primaryair channels 13. The outlet slots 14 of the said channels extend inradial direction, which is however not apparent from the drawing.

The flame bowl bottom 11 is further perforated for receiving on the onehand the ionization probe 15 and on the other hand the ignitionelectrodes 16 of which only a single one is shown in the drawing.

The cylindrical portion 10 of the flame bowl and the jacket tube 4 formbetween them an annular channel 17 for guiding the secondary air. Thisring channel tapers at 18 between the portion 7 of the jacket tube 4 andthe upper edge 19 of the cylindrical portion 10. Upstream of the annularchannel 17, there are provided whirling means 20 for the secondary airwhich comprise a ring 21 with oblique channels 22 extending therein.

The cylindrical portion 10 is likewise provided with whirl-generatingslot-like channels 24 through which secondary air enters the flame bowl9 from the annular space 17. The free passage 18 may be varied as afunction of the axial position of the burner tip insert 3 relative tothe jacket tube 4, so that a more or less big throttle is obtained. Thegreater the throttle at 18, the greater is the volume of air flowinginto the flame bowl via the channels 24. Thus, the secondary air volumecan be subdivided in a simple manner.

The geometry of the flame changes depending on the air volume enteringthe flame bowl 9 through the channels 13 and/or 24. In this manner theflame can be adapted very easily to the respective combustion chamber.The fact that the primary air leaves the channel 13 partly in the radialdirection prevents in addition any coking in the area of the nozzleoutlet. Due to the favorable air paths of the whirls and theircoordination, a conductivity sufficient for ionization flame control isobtained already in the flame bowl 9 so that a very compact design canbe achieved.

In the variant shown in FIG. 3, the bottom 11 of the flame bowl 9 has astepped design, comprising an outer ring 30 and an inner ring 31. Theouter ring 30 is recessed in the direction of flow and receives theionization probe 15 and the ignition electrodes 16. The slot-shapedchannels 24 open into the flame bowl a short distance above the bottomof the outer ring bottom 30 so that this first section of openings isarranged opposite the cylindrical wall 34 formed by the step.

The inner ring 31 is provided with a ceramic coating 33 to prevent anysoot layers from sticking to this point which must be kept cool becauseof the nozzle.

I claim:
 1. Process for producing a sootless flame in a pressureatomizer burner having an oil nozzle for producing an oil atomizingcone, primary air supply channels for supplying a primary air whirlaround and in the direction of the atomizing cone and secondary airsupply channels for supplying a secondary air whirl around andtransversely inwardly toward the primary air whirl, the processcomprising the step of supplying at least a major portion of the primaryair via primary air supply channels having outlets radially outwardly ofthe outlet of the oil nozzle adjacent to the transverse plane of thenozzle outlet to produce a primary air whirl around the oil atomizingcone from adjacent the plane of the nozzle outlet and further comprisingthe step of selecting the flow rates of air via both the primary andsecondary air supply channels to provide said primary and secondary airwhirls at selected strengths for controlling the length and width of theburner flame.
 2. A process according to claim 1 wherein a burner flamesufficient for ionization control is obtained adjacent said transverseplane of the nozzle outlet.
 3. A process according to claim 1 whereinthe outlets of the secondary air supply channels extend in part upstreamof the oil atomizing cone and the said outlets of the primary air supplychannels.
 4. An oil burner having a jacket tube and a burner nozzleassembly mounted coaxially within the jacket tube comprising an oilnozzle for producing an oil atomizing cone, a flame bowl having a bottomwith axial air supply means with outlets for supplying a primary airwhirl downstream around the atomizing cone from adjacent the transverseplane of the outlet of the oil nozzle and between the nozzle outlet andatomizing cone, the flame bowl having a generally cylindrical peripheralwall, the peripheral wall and jacket tube defining an annular channeltherebetween for guiding tertiary air to the burner flame downstream ofthe flame bowl, radial air supply means in the peripheral wall forsupplying air from the annular channel to the interior of the flame bowlfor supplying secondary air to the oil burner flame, and air whirlingmeans upstream of said radial air supply means, the radial air supplymeans comprising axially extending slot-shaped channels provided in theperipheral wall of the flame bowl obliquely relative to a peripheralwall tangent for imparting an angular whirl to the secondary air flowingfrom the annular channel into the flame bowl, the axial air supply meanscomprising radial channels in the bottom of the flame bowl having atleast sections thereof with said outlets and with a helical shape forproducing said primary air whirl.
 5. An oil burner according to claim 4wherein the transverse plane of the oil nozzle outlet is recessedupstream very slightly relative to the outlets of the axial air supplymeans.
 6. An oil burner according to claim 4 wherein at least the saidsections of the radial channels have radial inlets and/or outlets.
 7. Anoil burner according to claim 4 wherein the said sections of the radialchannels are provided within a replaceable ring insert fixed around theoil burner nozzle.
 8. An oil burner according to claim 4 wherein thejacket tube converges inwardly in the downstream direction at thedischarge end thereof to form with the downstream end of the peripheralwall of the flame bowl a generally conical air passage for throttlingthe tertiary air.
 9. An oil burner according to claim 8 wherein theflame bowl is displaceable axially relative to the jacket tube to varythe cross-section of the said generally conical air passage.
 10. An oilburner according to claim 4 wherein said air whirling means for thesecondary and tertiary air is upstream of said annular channel.
 11. Anoil burner according to claim 4 further comprising a flame controlsensor and an ignition electrode arranged within the flame bowl.
 12. Anoil burner according to claim 11 wherein the flame control sensorcomprises an ionization probe which coacts with the flame bowl as agrounded pole.
 13. An oil burner according to claim 11 wherein thebottom of the flame bowl comprises a central annular portion having saidaxial air supply means and an outer annular portion recessed in theupstream direction relative to said central annular portion andreceiving the sensor.
 14. An oil burner according to claim 11 wherein atleast certain sections of the interior of the flame bowl have a heatinsulating layer of ceramic or oxide ceramic material.